Dispensers for dispensing one or more components are known and are made in a variety of different sizes. Conventional methods of expelling material from a twenty liter dispenser comprise pressurising the air space above the component in the dispenser. Usually a piston is inserted between the pressurised air and the component to be dispensed to prevent cavitation and loss of efficiency of expulsion. However, it is common for the pressurised air to still leak past the piston which is undesirable. Our copending Australian patent application 56206/90 discloses the use of an air bag to contain pressurised air, together with the use of a central rod to prevent bowing of the ends of the container. Whilst the invention disclosed in that application does provide adequate dispensing of components we have found that in some instances the bags burst unless prohibitably expensive materials are used. This bursting can be exacerbated because of the need of the air bag to wrap around the center rod which causes localized stresses.
The object of this invention is to overcome this problem.